The present invention relates to a floppy disk apparatus (also known as floppy disk drive) used in information processing systems and others.
Control of a floppy disk loaded in the floppy disk drive or apparatus known heretofore is performed by a random logic which uses a gate array to provide functions which can be programmed either during manufacture or in the field. In the case of the former, the setting of signal selection for the logic processing can be optionally changed by using a switch or by connecting a chip resistor or the like measures.
FIG. 3 of the accompanying drawings is a block diagram showing a hitherto known logic circuit designated for changing the signal selection by using a switch. In this figure, a reference numeral 1 denotes a switch having one end connected to the ground and the other end which is connected to a second input terminal of an AND gate 2 and a second input terminal of another AND gate 4 through an inverter 3, and a numeral 5 denotes a resistor connected between the input of the inverter 3 and a power supply of +5 volts.
Applied to the first input terminal of the AND gate 2 is a ready signal, while applied to a first input terminal of the AND gate 4 is a disk-in signal.
A reference numeral 6 denotes an OR gate which serves to select either the ready signal output from the AND gate 2 or the disk-in signal output from the AND gate 4 to thereby produce the selected signal as an interface output signal. AND gates 2 and 4 and OR gate 6 together form a multiplexer.
In operation of the logic circuit shown in FIG. 3, when the switch 1 is closed thereby to form a short-circuit to the ground, the level at the input terminal of the inverter 3 becomes low, which results in a high level at the second input terminal of the AND gate 4. When the disk-in signal is applied to the first input terminal of the AND gate 4 in this state, the disk-in signal is selected by the OR gate 6 to be output as the interface output signal.
The disk-in signal is a signal which informs a host system of the state in which a medium or a floppy disk has been inserted in the floppy disk drive.
When the switch 1 is opened, the high level makes appearance at the second input terminal of the AND gate 2, while the level appearing at the second input of the AND gate 4 becomes low. Accordingly, when the ready signal is applied to the first input terminal of the AND gate 2 in this state, the ready signal is selected by the OR gate 6 to be output as the interface output signal.
This ready signal is used to inform the host system of the state in which the medium or disk has been placed in the floppy disk apparatus with a spindle motor rotating at a constant speed and thus the floppy disk apparatus is now ready for a read/write operation.
FIG. 4 of the accompanying drawings is a block diagram showing a hitherto known logic circuit which is arranged to change the signal selection by selectively mounting a chip resistor. In FIG. 4, like parts or elements as those shown in FIG. 3 are denoted by like reference numerals. The following description will be directed to those parts which differ from those of the logic circuit shown in FIG. 3.
Referring to FIG. 4, a reference numeral 7 denotes a chip resistor which is connected between terminals 8b and 8c of a printed circuit substrate (not shown), wherein the terminal 8a is connected to a power supply of +5 volts while the terminal 8c is connected to the ground.
A numeral 9 denotes a light emission diode which is mounted on a front panel of a floppy disk drive or apparatus for indicating that the apparatus is in an in-service state, when it is lit. The light emission diode 9 is energized in response to an in-use interface signal. A numeral 10 denotes a resistor of 270 .OMEGA. connected between the light emission diode 9 and the power supply of +5 volts.
Description will be made of operation of the prior art logic circuit shown in FIG. 4. Because of the chip resistor 7 inserted between the terminals 8b and 8c, both the input terminal of the inverter 3 and the second input terminal of the AND gate 2 assume a low level while the second input terminal of the AND gate 4 assumes a high level.
Accordingly, the in-use signal applied to the first input terminal of the AND gate 4 is selected by the OR gate 6 to be output as the interface output signal, which results in lighting of the light emission diode 9 indicating that the floppy disk apparatus is now being used.
On the other hand, when the chip resistor 7 is positioned between the terminal 8a and the terminal 8b, the second input terminal of the AND gate 2 assumes a high level with the second input of the AND gate 4 being at low level.
Accordingly, when a drive select signal is applied to the first input terminal of the AND gate 2 in this state, the drive select signal is selected by the OR gate 6 thereby to energize the light emission diode 9.
The in-use signal mentioned above serves to energize the light emission diode 9 indicating that the floppy disk apparatus is being used. On the other hand, the drive select signal is used for indicating that the floppy disk apparatus is selected by the host system to which it is connected.
As is apparent from the above, in the case of the prior art logic circuit shown in FIG. 3, the switch must be correspondingly turned on/off when it is desired to change the signal selection of the logic circuit.
On the other hand, in the case of the prior art logic circuit shown in FIG. 4, the chip resistor 7 has to be mounted or remounted by brazing when the signal selection of the logic circuit is to be changed. Accordingly, in order to verify the operation of the printed circuit set at a particular signal selection mode, it is necessary to visually verify whether the part of concern is actually mounted or positioned properly or to determine the signal selection mode.
Further, in both the logic circuits shown in FIGS. 3 and 4, difficulty will be encountered in performing inspection and adjustment of the floppy disk apparatus set at different signal selection modes while making verification in the course of manufacturing process.